How do you solve the following system: x + 8y = 15 , x + 4y = -2 x+8y=15,x+4y=−2?

1 Answer
Topscooter
Dec 18, 2015

x = -19x=−19
y = 17/4y=174

Explanation:

You can already say with the 2nd equation that x = -2 - 4yx=−2−4y.

You replace x by its new expression in the 1st line :

x + 8y = 15 iff -2 - 4y + 8y = 15 iff 4y = 17 iff y = 17/4x+8y=15⇔−2−4y+8y=15⇔4y=17⇔y=174

You now replace y by its value in the second equation !

x = -2 - 4y iff x = -2 - 17 iff x = -19x=−2−4y⇔x=−2−17⇔x=−19

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